Linear polyesters such as poly(alkylene terephthalate) are generally known and commercially available where the alkylene typically has 2 to 8 carbon atoms. They have many valuable characteristics including strength, toughness, high gloss and solvent resistance. Linear polyesters are conventionally prepared by the reaction of a diol with a dicarboxylic acid or its functional derivative, typically a diacid halide or ester. Linear polyesters may be fabricated into articles of manufacture by a number of known techniques including extrusion, compression molding, and injection molding.
Recently, macrocyclic polyester oligomers were developed which have unique properties. These properties make them attractive as matrices for engineering thermoplastic composites. These desirable properties stem from the fact that macrocyclic polyester oligomers exhibit low melt viscosity, allowing them to impregnate a dense fibrous preform easily. Furthermore, certain macrocyclic polyester oligomers melt and polymerize at temperatures well below the melting point of the resulting polymer. Upon melting and in the presence of an appropriate catalyst, polymerization and crystallization can occur virtually isothermally. As a result, the time and expense required to thermally cycle a tool is favorably reduced.
Development of processing equipment for use with macrocyclic polyester oligomers has been limited. It is generally believed that production of molded parts from macrocyclic polyester oligomers requires existing equipment to be modified to allow for transfer of the macrocyclic polyester oligomers and polymerization catalysts into the equipment in the appropriate amounts at the appropriate time and at the appropriate temperature. Modifying existing equipment takes time and is often costly, and hence limits the application of macrocyclic polyester oligomers.